Catalytic combustion systems are well known in gas turbine applications to reduce the formation of pollutants in the combustion process. As known, gas turbine engines include a compressor for compressing air, a combustion stage for producing a hot gas by burning fuel in the presence of the compressed air, and a turbine for expanding the hot gas to extract shaft power. Catalytic oxidation reactions involve the flowing of a mixture of fuel and air over a catalytic material and the reaction of the fuel, e.g. methane, syngas, with the catalytic material to release the partially-oxidized fuel components back to the fuel-air mixture. Partial pre-oxidation of the fuel prior of final burning helps to control the stability and efficiency of fuel burning in the combustor, and helps to significantly reduce the amount of developed NOx to below the 3 ppm level.
U.S. Pat. No. 6,174,159 describes a catalytic oxidation method and apparatus for a gas turbine engine utilizing catalytic combustion with a backside cooled design. In such combustors, multiple cooling conduits, such as tubes, are coated on the outside diameter with a catalytic material and are disposed in a catalytic reactor portion of the combustor. A small portion of air is mixed with fuel, then the mixture is directed over the conduits coated with catalytic material, and, as a result of an exothermic catalytic reaction of fuel species with the catalytic material, fuel is partially oxidized. Simultaneously, a main portion of air is separated by being passed through the conduits. The main portion of air has a temperature much lower than the temperature developed on the surface of catalytic elements and serves as a cooling media in the catalytic module. The hot, partially-oxidized fuel-air mixture then exits the catalytic chamber and is mixed with the cooling air that was directed through tubes, creating a uniformly heated, partially pre-oxidized, and homogeneous combustible mixture.
Multi-component or heterogeneous catalysts comprising a combination of metals and metal oxides have recently been employed as the catalytic material in a number of catalytic combustion systems because of their advantages over monometallic catalysts. For example, a Pt—Pd catalyst system provides improved stability compared to a monometallic catalyst (Pd or Pt only) system and the Pt—Pd catalyst system is able to oxidize methane at a higher rate than a monometallic catalyst system. One drawback, however, for many catalytic systems is that they typically have high ignition temperatures or temperatures at which the catalytic reaction is able to be started. Ignition or start-up temperature of catalytic reaction is an important characteristic of a catalyst. Catalyst ignition starts the partial oxidation of fuel. When attempting to ignite at lower temperatures, e.g. at temperatures of the compressed air fed from the compressor outlet of the engine, higher concentrations of active components in a catalytic material are required to start the catalytic reaction. Thus, another drawback of known catalyst systems employing any catalytic system is that they require substantial amounts of expensive transition metals to obtain a start-up of catalytic reactions at such lower temperatures. There remains a need for low cost catalytic systems that meet low temperature ignition criteria.